common ion effect Q

[cloak25]

What is observed when sodium carbonate is added to a saturated calcium hydroxide solution with undissolved calcium hydroxide on the bottom of the flask?

A. The pH of the solution will increase more than it would increase had it been added to an unsaturated solution of calcium hydroxide.
B. The pH of the solution will increase less than it would increase had it been added to an unsaturated solution of calcium hydroxide.
C. The pH of the solution will decrease more than it would decrease had it been added to an unsaturated solution of calcium hydroxide.
D. The pH of the solution will decrease less than it would decrease had it been added to an unsaturated solution of calcium hydroxide.

Answer: A Can someone explain choice A in a different way? I understand the concept of common ion effect but not sure what they're saying when they say "had it been added to an unsaturated solution of calcium hydroxide.."

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[MedPR]

What is observed when sodium carbonate is added to a saturated calcium hydroxide solution with undissolved calcium hydroxide on the bottom of the flask?

A. The pH of the solution will increase more than it would increase had it been added to an unsaturated solution of calcium hydroxide.
B. The pH of the solution will increase less than it would increase had it been added to an unsaturated solution of calcium hydroxide.
C. The pH of the solution will decrease more than it would decrease had it been added to an unsaturated solution of calcium hydroxide.
D. The pH of the solution will decrease less than it would decrease had it been added to an unsaturated solution of calcium hydroxide.

Answer: A Can someone explain choice A in a different way? I understand the concept of common ion effect but not sure what they're saying when they say "had it been added to an unsaturated solution of calcium hydroxide.."

When you add the sodium carbonate it is going to react with the dissolved calcium hydroxide as well as the solid calcium hydroxide and add more hydroxide to the solution as sodium hydroxide. If the solution was unsaturated, there would not be any solid calcium hydroxide to react with, so the pH really wouldn't change much since you would just be interconverting between NaOH and Ca(OH)2. However, with the saturated solution, the Na2CO3 reacts with the solid Ca(OH)2 (which as a solid does not contribute to the pH) and becomes NaOH(l) or NaOH(aq) which will contribute to the pH.